Hyperthermia and cardiovascular strain during an extreme heat exposure in young versus older adults

Abstract

We examined whether older individuals experience greater levels of hyperthermia and cardiovascular strain during an extreme heat exposure compared to young adults. During a 3-hour extreme heat exposure (44°C, 30% relative humidity), we compared body heat storage, core temperature (rectal, visceral) and cardiovascular (heart rate, cardiac output, mean arterial pressure, limb blood flow) responses of young adults (n = 30, 19–28 years) against those of older adults (n = 30, 55–73 years). Direct calorimetry measured whole-body evaporative and dry heat exchange. Body heat storage was calculated as the temporal summation of heat production (indirect calorimetry) and whole-body heat loss (direct calorimetry) over the exposure period. While both groups gained a similar amount of heat in the first hour, the older adults showed an attenuated increase in evaporative heat loss (p < 0.033) in the first 30-min. Thereafter, the older adults were unable to compensate for a greater rate of heat gain (11 ± 1 ; p < 0.05) with a corresponding increase in evaporative heat loss. Older adults stored more heat (358 ± 173 kJ) relative to their younger (202 ± 92 kJ; p < 0.001) counterparts at the end of the exposure leading to greater elevations in rectal (p = 0.043) and visceral (p = 0.05) temperatures, albeit not clinically significant (rise < 0.5°C). Older adults experienced a reduction in calf blood flow (p < 0.01) with heat stress, yet no differences in cardiac output, blood pressure or heart rate. We conclude, in healthy habitually active individuals, despite no clinically observable cardiovascular or temperature changes, older adults experience greater heat gain and decreased limb perfusion in response to 3-hour heat exposure.

No effect of ascorbate on cutaneous vasodilation and sweating in older men and those with type 2 diabetes exercising in the heat

“…As such, we were also able to assess the influence of a passive heat stress on heat loss responses which has been shown to be attenuated in older adults with (Kenny et al. ) and without type 2 diabetes (Kenny et al. ) relative to young adults.…”

“…; Kenny et al. ). In parallel, although nitric oxide (NO) synthase (NOS) is known to contribute to the regulation of cutaneous vasodilation (Kellogg et al.…”

Folic acid supplementation does not attenuate thermoregulatory or cardiovascular strain of older adults exposed to extreme heat and humidity

“…Studies employing whole‐body direct calorimetry have demonstrated that older adults store more heat during simulated heat wave conditions relative to young adults (Kenny et al., ; Stapleton et al., ). Interestingly, greater heat storage in older adults was mediated solely through greater dry heat gain in these studies as sweat evaporation was similar to young adults.…”

Ageing of the carotid body

“…The ventilatory and heart rate responses to hypoxia and hypercapnia diminish in old age, with a reduction in adrenergic responses (Kenny et al . ). The age‐dependent reduction in breathing capacity is evident, causing tissue hypoxia.…”